The electrically adjustable antenna for a base station facilitates tilt adjustment of a beam of the base station antenna via a phase shifter in beam-forming networks, characterized in wide-range tilt adjustment, high precision, easily-managed direction pattern, strong capacity of resisting disturbance, and easy control. The Phase shifter acting as an essential component of base station antenna can adjust tilt angle of an antenna beam by changing the relative phase between antenna units, thus providing an improved communication network. In principle, a beam-forming network for electrically adjustable antenna can be formed in two methods. One is to insert a dielectric into feed line to alter the dielectric constant during transmission, thus to change the wavelength of the electromagnetic wave to suit the change of the travelling electromagnetic wave, meaning the change of the feed phase. Thus changing the wavelength of the electromagnetic wave is equivalent to a change in the feed phase. The change of feed phase refers to the fact that if the length of the feed striplines is changed a small amount, then there will be a big change in the phase shift, relative to the first scenario. The other is to alter the length of feed lines either by increasing or decreasing, which means to increase or decrease the route of electromagnetic wave directly so as to change the feed phase, wherein the changes to the feed lines are small and loss is minimal, yet some implementations would cause non-linear changes of the phase, complicated achievement or bad intermodulation.
A beam-forming network is previously known in U.S. Pat. No. 5,949,303, wherein phase shift is achieved by a dielectric member moving between a substrate and meander-shaped feed network, and the phase difference between different output ports achieved by transmission line dielectric of the feed network covering different lengths. The disadvantage: the meander-shaped loops are parallel so the device is relatively large in the lateral direction. Further, the relative position of output break, that is the relative position of the output port, will affect distribution, which goes against reducing signal reflection and designing components with broadband response, and adding to the complexity of phase shifter structure, even in contradiction with reality in some applications.
A beam-forming network is previously known in CN1547788A, wherein the phase shift among a plurality of ports is achieved by relative sliding between a highly-integrated circuit board and thin dielectric plate, similar to that described in U.S. Pat. No. 5,949,303. However, it is difficult to guarantee that the too-thin dielectric plate will remain the same due to the material and mechanical strength, and the phase shifter may get completely jammed or the phase shift precision may be affected due to an uneven force that the deformed dielectric plate created as a result of the movement. This is because the deformed dielectric plastic plate will bear uneven force when moving.
As stated previously, current technology apparently encounters defect and inconvenience in actual use. Yet the fast-pacing mobile communication technology advances the trend of miniaturization, broadband and multi-frequency related to base station antenna, demanding new phase shifter structures of low-cost but high performance to deal with the said issues.